Anti-inflammatory drug pirprofen (PF) is an amphoteric which contains a nitrogen atom and a carboxyric acid group. PF is practically insoluble in water and not stable enough (against moisture, temperature, light) for a certain dosage form, having an irritant sensation on the throat mucosa. These undesirable properties of PF were found to be improved effectively by forming an inclusion complex with β-cyclodextrin (β-CyD). The molar ratio of PF-β-CyD complex was 1 : 1 in dilute aqueous solution, while 2 : 3 in solid state. The stability constant of complex changed with pH value, and it gave a maximum value at pH 7.5. The different inclusion mode of complex in acidic and alkaline solutions was proposed by means of various spectroscopies. The increase in dissolution rate of PF by β-CyD complexation was rather small in acidic medium, because of the dissociation of complex. The bioavailability of inclusion complex was compared with that of PF alone after oral administration to dogs and it was found that the plasma level of PF was almost equal in both cases.
